The parent invention relates to electrophysiology apparatus which is used to measure and to visualize electrical activity occurring in a patient""s heart. The system can display both a visual map of the underlying electrical activity originating in a chamber of a patient""s heart and the location of a therapy catheter located within a heart chamber. The electrophysiology apparatus includes several subsystems including: a therapy catheter system, a measurement catheter system and a computer based signal acquisition, control and display system.
Many cardiac tachyarrhythmias are caused by conduction defects which interfere with the normal propagation of electrical signals in a patient""s heart. These arrhythmias may be treated electrically, pharmacologically or surgically. The optimal therapeutic approach to treat a particular tachyarrhythmia depends upon the nature and location of the underlying conduction defect. For this reason electrophysiologic mapping is used to explore the electrical activity of the heart during a tachyarrhythmic episode. The typical electrophysiologic mapping procedure involves positioning an electrode system within the heart. Electrical measurements are made which reveal the electrical propagation of activity in the heart. If ablation is the indicated therapy then a therapy catheter is positioned at the desired location within the heart and energy is delivered to the therapy catheter to ablate the tissue.
There are numerous problems associated with these electrophysiologic diagnostic and therapeutic procedures. First the testing goes on within a beating heart. The motion of the diagnostic catheter and treatment catheter can injure the heart and provoke bouts of arrhythmia which interfere with the collection of diagnostic information. During the delivery of ablation therapy it is common to use fluoroscopic equipment to visualize the location of the catheters. Many physicians are concerned about routine occupational exposure to X-rays. In addition, the traditional mapping techniques do not provide a high resolution view of the electrical activity of the heart which makes it difficult to precisely locate the source of the arrhythmia.
The electrophysiology apparatus of the invention is partitioned into several interconnected subsystems. The measurement catheter system introduces a modulated electric field into the heart chamber. The blood volume and the moving heart wall surface modify the applied electric field. Electrode sites within the heart chamber passively monitor the modifications to the field and a dynamic representation of the location of the interior wall of the heart is developed for display to the physician. Electrophysiologic signals generated by the heart itself are also measured at electrode sites within the heart and these signals are low pass filtered and displayed along with the dynamic wall representation. This composite dynamic electrophysiologic map may be displayed and used to diagnose the underlying arrhythmia.
A therapy catheter system can also be introduced into the heart chamber. A modulated electrical field delivered to an electrode on this therapy catheter can be used to show the location of the therapy catheter within the heart. The therapy catheter location can be displayed on the dynamic electrophysiologic map in real time along with the other diagnostic information. Thus the therapy catheter location can be displayed along with the intrinsic or provoked electrical activity of the heart to show the relative position of the therapy catheter tip to the electrical activity originating within the heart itself. Consequently the dynamic electrophysiology map can be used by the physician to guide the therapy catheter to any desired location within the heart.
The dynamic electrophysiologic map is produced in a step-wise process. First, the interior shape of the heart is determined. This information is derived from a sequence of geometric measurements related to the modulation of the applied electric field. Knowledge of the dynamic shape of the heart is used to generate a representation of the interior surface of the heart.
Next, the intrinsic electrical activity of the heart is measured. The signals of physiologic origin are passively detected and processed such that the magnitude of the potentials on the wall surface may be displayed on the wall surface representation. The measured electrical activity may be displayed on the wall surface representation in any of a variety of formats. Finally, a location current may be delivered to a therapy catheter within the same chamber. The potential sensed from this current may be processed to determine the relative or absolute location of the therapy catheter within the chamber.
These various processes can occur sequentially or simultaneously several hundred times a second to give a continuous image of heart activity and the location of the therapy device.